Answer: B. Constant current driver chip.
Answer analysis: When discussing the question of which chip determines the grayscale level of the LED screen, we must first understand the grayscale level and the basic principles of the LED screen. Grayscale refers to the brightness level that can be distinguished from the darkest to the brightest in the single primary color brightness of the LED display. The higher the grayscale level, the richer the color, the more delicate the picture, and the higher the requirements for the display control system.
Now, let's analyze the options one by one:
A. Row tube: Row tube, also known as row driver tube or row output tube, is usually used in the row scanning circuit of a TV. In the LED display, it does not directly determine the grayscale level, but is responsible for controlling whether a certain row of the display is lit. Therefore, the row tube has no direct relationship with the grayscale level.
B. Constant current driver chip: In the LED display, each LED lamp requires a stable current to ensure its brightness and color consistency. The constant current driver chip is used to provide a stable current for the LED. Since the realization of grayscale depends on the precise control of LED brightness, and the control of brightness depends on the stability of current, constant current driver chips play a vital role in the grayscale control of LED display screens.
C. 245: 245 chips usually refer to buffers/drivers such as 74HC245 or 74HCT245, which are mainly used for bidirectional buffering and driving of data. Although they play an important role in data transmission, they do not directly determine the grayscale of LED display screens.
D. Flash: Flash memory is mainly used to store data, such as firmware, configuration files, etc. It has no direct relationship with the grayscale control of LED display screens.
In summary, the grayscale of LED screens is mainly determined by constant current driver chips, because constant current driver chips are responsible for providing stable current to LEDs, thereby ensuring the stability of LED brightness and color, which is the basis for achieving high-precision grayscale.
Therefore, the correct answer is B. constant current driver chip.